시계 만들기

• Clock.jsx

import React from "react";

function Clock(props) {
	return (
		<div>
			<h1>hello, react!</h1>
			<h2>current time: {new Date().toLocaleTimeString()}</h2>
		</div>
	);
}

export default Clock;

• index.js

import React from 'react';
import ReactDOM from 'react-dom/client';
import './index.css';
import App from './App';
import reportWebVitals from './reportWebVitals';
import Clock from './chapter_04/Clock';

const root = ReactDOM.createRoot(document.getElementById('root'));

setInterval(() => {
  root.render(
    <React.StrictMode>
      <Clock />
    </React.StrictMode>
  );
}, 1000);


// If you want to start measuring performance in your app, pass a function
// to log results (for example: reportWebVitals(console.log))
// or send to an analytics endpoint. Learn more: https://bit.ly/CRA-vitals
reportWebVitals();

1초당 계속해서 엘리먼트가 렌더링 되고 있는 부분을 볼 수 있다.